Fix COG custom colormap bug

[giswqs]

Fix #867

import leafmap

url = "https://clarkcga-aquaculture.s3.amazonaws.com/data/el_salvador/cover/El_Salvador_Landcover_2022.tif"
custom_cmap = {
    "0": "#000000",
    "1": "#008040",
    "2": "#ff0000",
    "3": "#ffff00",
    "4": "#8000ff",
    "5": "#8080ff",
    "6": "#00ff00",
    "7": "#c0c0c0",
    "8": "#16002d",
    "9": "#ff80ff",
    "10": "#b3ffb3",
    "11": "#ff8080",
    "12": "#ffffbf",
    "13": "#000080",
    "14": "#808000",
    "15": "#00ffff",
}
m = leafmap.Map()
m.add_cog_layer(url, colormap=custom_cmap, name="El_Salvador")
legend_dict = dict(zip([int(key) for key in custom_cmap.keys()], custom_cmap.values()))
m.add_legend(title="Landcover", legend_dict=legend_dict)
m

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